C:N:P stoichiometry of plant-soil-microbe in the secondary succession of zokor-made mounds on Qinghai-Tibet Plateau

Abstract

The knowledge of ecological stoichiometry and stoichiometric homeostasis could contribute to exploring the balance of chemical elements in ecological recovery. However, it is largely unknown how the carbon (C), nitrogen (N), phosphorus (P), and stoichiometric characteristics in the plant-soil-microbe continuum system respond to the spontaneous secondary succession of degraded alpine grasslands. Therefore, we investigated the spontaneous secondary successional recovery of grasslands disturbed by zokor (Myospalax fontanierii) on the Qinghai-Tibetan Plateau, China, via a strategy of substituting space for time. Based on plant richness, biomass, and coverage, plant importance value was employed to assess the recovery degree of zokor-made mounds (ZMMs, large and bare patch areas constructed by zokors). Multiple statistical methods, including stoichiometric homeostatic model, network, and redundancy analysis, were conducted to decipher the stoichiometric patterns. The results indicated that plant C, C:N, and C:P increased with the recovery of ZMMs, contrary to the decrease of plant N and P. In addition, soil C, N, C:N, C:P, and N:P increased with the recovery degree, and the soil became relatively more N rich by increasing organic N under the revegetation of legumes. Meanwhile, soil microbial biomass C, N, and P increased with the recovery of ZMMs, but microbial biomass C:N:P ratios were highly constrained. Soil accessible inorganic nitrogen played an important role in driving plant and microbial nutrient and stoichiometry. Our results demonstrated that the different responses of C, N, and P contents in plant-soil-microbe lead to shifts in C:N:P stoichiometric ratio. Nevertheless, plants and soil microbes exhibited strong stoichiometric homeostasis. Collectively, our study provides new insight into biogeochemical responses to the successional recovery of degraded alpine grassland on the Qinghai-Tibetan Plateau from a stoichiometric perspective.